KIMM DVIA-PB2200 High-Frequency Amplification Issue Field Analysis Report (VOC26-049)

Report title: VOC26-049 – Korea Institute of Machinery & Materials, Field Analysis Report

Vibration isolation system: DVIA-PB2200, serial number 250122R1-1

Task leader: Sungyoon Jung

Engineers in charge: Donhyuk Jeon, Sungyoon Jung, Gyumin Park

Author: Sungyoon Jung

Report written date: 2026-07-07

This report was prepared to present the field measurement results and the technical root-cause analysis for the peak issue (VOC26-049) that occurred on the DVIA-PB2200 delivered to Korea Institute of Machinery & Materials (KIMM), in specific frequency bands (28 Hz on the X axis, 50 to 90 Hz on the X/Y/Z axes).

Vibration data were collected during a site visit on the actual unit (PB2200) while the support condition was varied.

Measurement items: Compliance, Passive transmissibility, Open-Loop frequency response function, Autospectrum, VC Curves

Support condition variations: 1) Levelfoot and Footmaster supporting together, 2) Levelfoot only (Footmaster removed), 3) Footmaster only

Instrumentation used: PULSE 22, Impact Hammer, accelerometer (PCB 393B05)

Independence from the support condition: even when the floor support method was changed (Levelfoot, Footmaster and so on), the 28 Hz peak was confirmed to occur consistently on the X axis only. (It does not appear on the Y axis, and the amplification ratio on the Z axis is very low.)

Open-Loop phase analysis: at that frequency (28 Hz), the phase of the open-loop frequency response function crosses 0 degrees (phase crossover). In control engineering terms this is evidence of a structural resonance. In other words, the peak occurring in the 28 Hz band is not a malfunction of the active control system of the isolator or a software error. An abrupt phase change in the open loop means a structural resonance arising in a particular mechanical part of the overall system, that is the payload on top or the isolator table top coupled to it.

When the equation of motion of a single-degree-of-freedom mass-spring-damper (m-k-c) model is transformed into the frequency domain (s = jω), the denominator of the transfer function takes the following form: Denominator = k − mω² + jcω

Why the magnitude peak occurs: when the excitation frequency (ω) reaches the natural frequency (ωn = √(k/m)), the real part becomes 0 and takes its minimum value. When the denominator is minimum, the response magnitude forms its maximum value (peak).

Why the phase crossover occurs: the phase is determined by the ratio of the real part to the imaginary part, atan(cω / (k − mω²)). Below the natural frequency the real part is positive; above the natural frequency the real part is negative; at the natural frequency the real part passes through 0.

Equipment-dependent phenomenon (vibration transmitted from the payload): the fact that this peak appears independently and only in the X-axis direction regardless of the support condition suggests a high probability that an eccentric center of gravity of the payload itself, or structural shaking of an internal component (for example a vacuum pump), is being transmitted into the isolator table top.

Proposed follow-up verification (how to confirm the payload factor): the most reliable way to cross-check intuitively that this phenomenon comes from the structural directivity of the payload itself (a difference in X-axis and Y-axis stiffness) rather than from the isolator is proposed as follows. If the piping and wiring constraints of the payload allow it, the payload can be rotated 90 degrees using the Footmaster and measured in the same way. If the 30 Hz peak that used to occur on the X axis then appears on the Y axis after the rotation, this confirms with certainty that it is a characteristic of the payload itself (an equipment issue).

Measurement result: as the support condition (the floor support position of the Levelfoot, Footmaster and so on) was changed, a tendency for the resonance peak frequencies in the 50 to 90 Hz band to shift was observed. When both the Levelfoot and the Footmaster were lowered, the number of resonance peaks decreased. The more support points there are, the higher the resonance frequency rises.

Cause analysis: this tendency agrees with in-house testing and simulation (FEM) results, and is judged to be a mechanical structural resonance of the table top depending on the payload coupling condition.

FEM simulation conditions: the payload is assumed rigid, and the support parts of the payload (the parts emulating the Levelfoot and Footmaster) are assumed to be steel.

The photographs attached below show the levelness of the isolator table top; in addition, the levelness of the payload was confirmed to be at the 0 mm/min level.

The side chamber weighs 50 kg or less in total, which is very light compared with the equipment weight. The amount of eccentricity is negligible.

Noise measurement was performed at the center of the isolator table top. The measured 12.5 Hz noise was below 30 dB, a very small level. Therefore noise is not the cause of the 12.5 Hz active transmissibility amplification.

After removing all filters, the open-loop frequency response function was measured for each support condition.

Passive vs Active comparison: blue is Active, red is Passive.

Support condition comparison: blue is Levelfoot and Footmaster, red is Levelfoot, black is Footmaster.

The resonance frequencies above 20 Hz are identical for Active and Passive.

The 28 Hz peak on the X axis occurs regardless of the support condition.

28 Hz peak issue — Cause: the 28 Hz peak that stands out in the X-axis direction is presumed to originate from the structural characteristics of the pump drive section of the payload.

28 Hz peak issue — Action item: a structural analysis of the customer's pump drive section is expected to clarify the cause definitively.

50 to 90 Hz band peak issue — Cause: taking the FEM analysis and the field measurement results together, the amplification in this band is presumed to be a structural resonance caused by insufficient stiffness of the isolator table top.

50 to 90 Hz band peak issue — Action item: a fundamental solution to this issue requires reinforcement of the table top stiffness or reinstallation work.

However, because the vibration amplification ratio and the absolute vibration magnitude are small, it is judged that there will be no problem with the customer's equipment operation. Large-scale hardware modification work such as table top reinforcement will therefore be carried out on a paid basis only if required.